Generally, a clothes dryer is an apparatus for drying the laundry by blowing hot air generated by a heater into a drum to evaporate moisture contained in the laundry.
Such clothes dryers may be classified into an exhaust type clothes dryer and a condensation type clothes dryer depending on a method of treating humid air discharged from a drum after the laundry is dried by hot air.
The exhaust type clothes dryer uses a heater or the like to heat new air flowing from the outside of the dryer to it into the drum and exhaust air of high temperature and high humidity discharged from the drum to the outside of the dryer.
The condensing clothes dryer cools hot and humid air discharged from the drum down to a dew point temperature or less in a condenser without exhausting it to the outside of the dryer, so as to condense moisture contained in the humid air, and reheat air passing through the condenser by a heater to circulate the reheated air into the drum.
Here, in the exhaust type clothes dryer, since the humidity of the air discharged from the drum decreases as a drying time elapses, a loss of thermal energy of air, which is discharged to the outside without being used, increases.
Also, in the condensation type clothes dryer, a loss of thermal energy of the air discharged from the drum is caused during the process of condensing the humid air, and the air is reheated by using a separate heater and the like for drying, thereby lowering thermal efficiency.
Accordingly, in recent time, a heat pump dryer, which is provided with an evaporator, a compressor, a condenser, and an expansion valve, and heats air supplied into a drum by recollecting energy of air discharged from the drum, so as to enhance energy efficiency, has been developed.
FIG. 1 is a schematic view illustrating a washing and drying machine 10 having the related art heat pump system.
The washing and drying machine 10 with the heat pump system illustrated in FIG. 1 (see the following prior art document D1) includes a refrigerant circuit 11. The refrigerant circuit 11 includes a high pressure section extending from an outlet of a compressor 12 up to an inlet of an expansion valve 13 via a first heat exchanger (condenser; 14), and a low pressure section extending from an outlet of the expansion valve 13 up to an inlet of the compressor 12 via a second heat exchanger (evaporator; 15). The refrigerant circuit 11 also includes an auxiliary heat exchanger 16 and an auxiliary fan 17. The auxiliary heat exchanger 16 is a heat exchanger that cools refrigerant through heat exchange with external cold air (ambient air). The auxiliary fan 17 is a component for supplying the external cold air. The auxiliary fan 17 may be controlled according to parameters related to dry air for drying the laundry and the refrigerant, namely, air temperature at an inlet side of a drum 18, a refrigerant temperature (or refrigerant pressure) at a rear end of the condenser 14 and a front end of the evaporator 15, or may control the temperature and pressure. For example, when an amount of heat in the heat pump system is exceeded, the auxiliary fan 17 is turned on to remove the exceeded amount of heat, and thus the auxiliary heat exchanger 16 cools refrigerant discharged from the condenser 14. In order to prevent the auxiliary heat exchanger 16 from cooling the refrigerant more than necessary, the auxiliary fan 17 is turned off.
Efficiencies of the heat pump system and the drier 10 can be improved as the auxiliary fan 17 is controlled to be turned on/off by preset upper and lower limit values.
However, in the case of the prior art D1, one evaporator is used to remove moisture of hot and humid air discharged from the drum. However, as temperature of air passing through the evaporator gradually decreases toward a rear end of the evaporator, a temperature difference between the refrigerant and the air passing through the evaporator gradually decreases, which causes a reduction of dehumidifying capability of the evaporator and a delay of the drying time.
In the prior art D1, since the auxiliary fan 17 is turned on/off according to the preset upper and lower limit values, it is difficult to determine whether the auxiliary fan 17 is out of order. In particular, since the auxiliary fan 17 is in an almost stopped state in an eco-mode for energy saving, it is difficult for a user to distinguish whether the stopped state of the auxiliary fan 17 is due to the eco-mode or a breakdown (failure).
As a result, when the dryer 10 is continuously operated without knowing that the auxiliary fan 17 is stopped due to a failure, the dehumidifying capability of the evaporator 15 deteriorates and the drying time increases.
FIG. 2 is a schematic view illustrating a clothes dryer 20 (refer to the prior art document D2) having the related art auxiliary heat exchanger, and FIG. 3 is a perspective view illustrating a heat pump system mounted in the clothes dryer 20 of FIG. 2.
The clothes dryer 20 illustrated in FIG. 2 includes a drum 26, and a heat pump cycle for heating air by inducing refrigerant to a condenser 21, an expansion valve 22, an evaporator 23, and a compressor 24.
The heat pump cycle includes an auxiliary heat exchanger 25 to remove heat from the heat pump cycle. A blower 27 cools an auxiliary heat exchanger 25 and the compressor 24 by ambient air.
The ambient air passes through the auxiliary heat exchanger 25 via a first blower 28a, and then is externally discharged through a second blower 28b via a periphery of the compressor 24.
The blowers 27, 28a, and 28b are controlled in several steps or continuously. For example, the blowers 27, 28a, and 28b are controlled by varying revolutions per minute (RPMs) thereof. Further, the blowers 27, 28a, and 28b are controlled according to a change amount of a value T1, T2 or ΔT=T1−T2 in comparison with a target temperature T0. That is, parameters for controlling the blowers 27, 28a, and 28b are T1, T2, and ΔT=T1−T2, and the target temperature is T0.
However, according to the prior art D2, the first and second blowers 28a and 28b for blowing ambient air to the auxiliary heat exchanger 25 and the like are implemented as a box fan. Accordingly, the first and second blowers 28a and 28b are operated by a separate small motor disposed within the box fan, and power for driving the first blower 28a and the second blower 28b is further required, which results in increasing energy consumption.
For the related art structure of the blowers 27, 28a, and 28b, their motors are controlled to be turned on/off according to a temperature signal sensed by a temperature sensor or the like, and an on/off signal is unilaterally transmitted to the motors. Accordingly, it is difficult to determine whether the blowers 27, 28a, and 28b are out of order, and accordingly it is difficult to cope with changes in product performance (performance of the heat pump cycle).